1. Field of the Invention
The present invention relates to a sample treatment apparatus, particularly to a sample treatment apparatus for applying a predetermined treatment to a liquid sample containing a particle component.
2. Description of the Prior Art
To measure sizes of and the number of particulates, microorganisms, or organic cells, sample measurement apparatuses have been used so far which use the "electrical-resistance-type particle measuring method", "sedimentation-type particle measuring method", and "light-scattering diffraction-type particle measuring method".
These apparatuses are marked with, for example, "For the particle concentration of 1,000 particles/.mu.l or more: measurement reproducibility (random error) of 10% or less" in order to assure the measurement precision (reproducibility or accuracy). It is generally accepted that measurement precision decreases (measurement reproducibility value increases) as the particle concentration decreases.
Therefore, to improve the measurement precision for a liquid sample with a low particle concentration, the following methods are used.
(i) To increase the number of particles to be measured by extending the measuring time.
(ii) To raise the particle concentration by previously centrifuging a sample to be measured and removing the supernatant liquid.
In the case of a sample measuring apparatus using the method of "extending the measuring time" in Item (i) , for example, the extensible measuring time is set to a value of 2 to 3 times larger than the standard measuring time. That is, the extension of the measuring time is limited. In addition, when the concentration of particles to be measured is low, a preferable result is rarely obtained even if the measuring time is extended.
In the case of a particle analyzer such as a flow cytometer, for example, the measuring time is approx. 10 sec because of the limitations of the apparatus, and thereby the measurable amount of a sample is limited to 2 to 3 .mu.l. Therefore, as for a sample with a particle concentration of approx. 1,000 particles/.mu.l, a stable result is obtained because the reproducibility (random error) comes to approx. 2%. As for a sample with a particle concentration of approx. 100 particles/.mu.l, however, inconsistent results are obtained because the measurement reproducibility comes to approx. 6%. Even if the measuring time is increased threefold, the reproducibility is improved only up to approx. 3%.
To measure the above sample at a reproducibility (random error) of approx. 2%, it is necessary to increase the measuring time 10 to 15 times or increase the sample concentration 10 to 15 times. However, because it is generally difficult to increase the measuring time tenfold, the measuring time has been increased only several times.
Therefore, a method of "measuring a sample once and thereafter measuring it again by setting a proper measuring time" is considered. However, this method has the disadvantage that measurement must be performed twice and therefore the operation is impractical.
Moreover, the method of "previously centrifuging a sample to be measured" in Item (ii) has the disadvantage that measurement must be performed at least twice paralleling the process of "preliminary measurement.fwdarw.treatment before actual measurement (e.g. centrifugal separation).fwdarw.actual measurement" and therefore the operation is considered to be impractical. Furthermore, the method has the disadvantage that a sample cannot be accurately analyzed when the amount of the sample is too small.
Recently, the necessity for measuring a sample of very small amount has been increased. In addition, in the case of a sample measuring apparatus such as a flow cytometer, though a sample of several hundred microliters is necessary, the actual amount of the sample to be measured is only several microliters, and therefore the bulk of the sample is wasted.
The present invention, "the Sample Treatment Apparatus", is designed to solve the above problems and its objective is to provide a sample treatment apparatus making it possible to execute a high measurement precision for a liquid sample of small amount without extending the measuring time or requiring any special pre-treatment.